Purified linear epitopes from cashew nuts, nucleic acids encoding therefor, and associated methods

ABSTRACT

Disclosed are major allergenic proteins in cashew nut, which are legumin-like proteins and 2S albumins. Also disclosed is a polypeptide allergen in the 7S superfamily, which includes vicilin-like and sucrose binding proteins. Several linear epitopes of the cashew nut are identified and characterized. The invention further discloses the sequence of cDNA encoding the allergenic polypeptide, the allergen being designated Ana o 1, and also describes the characterization of the expressed recombinant polypeptide and associated methods employing the polypeptide.

RELATED APPLICATION

This application is a continuation of and claims priority from utility application Ser. No. 10/264,303 (now U.S. Pat. No. 6,884,877), filed on Oct. 3, 2002, and which claimed priority from provisional applications Ser. No. 60/326,793, filed on Oct. 3, 2001, and Ser. No. 60/371,774, filed on Apr. 11, 2002, each priority application being incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of allergies to nuts and, more particularly, to purified linear epitope polypeptides from cashews, nucleic acids encoding therefor, and associated methods.

BACKGROUND OF THE INVENTION

It is estimated that up to 8% of children less than 3 years of age and 2% of adults are affected by food allergies. While food-induced allergic reactions are the most common cause of outpatient anaphylaxis, the majority of severe reactions of this kind are caused by peanuts and tree nuts. Most plant food allergens can be found among pathogenesis-related proteins, seed storage albumins and globulins, and α-amylase and protease inhibitors.

Cashew nuts have been associated with contact or systemic dermatitis (to cardol and anacardic acid found in the cashew nut shell oil¹), atopic dermatitis, and IgE-mediated systemic allergic reactions.²⁻⁴ Pistachios are another allergenic member of the Anacardiaceae family and show extensive in vitro cross-reactivity with cashews.^(5,6) Cashew nuts are widely used in snack foods and as an ingredient in a variety of processed foods such as bakery and confectionery products.

By sequencing of the N-termini and selected internal digests, we have found that the major allergenic proteins in cashew nut are legumin-like proteins and 2S albumins. We have also identified a polypeptide allergen in the 7S superfamily, which includes vicilin-like and sucrose binding proteins. Herein, we disclose the sequence of a CDNA encoding this allergenic polypeptide, designated Ana o 1, and describe the characterization of the expressed recombinant polypeptide. In addition, we identify several linear epitopes and compare these to the allergenic peanut vicilin, Ara h1.⁷

REFERENCES CITED

-   1. Marks J G Jr, DeMelfi T, McCarthy M A, Witte E J, Castagnoli N,     Epstein W L, Aber R C. Dermatitis from cashew nuts. J Am Acad     Dermatol 1984; 10: 627-31. -   2. Burks A W, James J M, Hiegel A, Wilson G, Wheeler J G, Jones S M,     Zuerlein N. Atopic dermatitis and food hypersensitivity reactions. J     Pediatr 1998; 132: 132-6. -   3. Tariq S M, Stevens M, Matthews S, Ridout S, Twiselton R, Hide     D W. Cohort study of peanut and tree nut sensitization by age of 4     years. BMJ 1996; 313: 514-7. -   4. Garcia F, Moneo I, Fernandez B, Garcia-Menaya J M, Blanco J,     Juste S, Gonzalo J. Allergy to Anacardiaceae: description of cashew     and pistachio nut allergens. J Investig Allergol Clin Immunol 2000;     10: 173-7. -   5. Fernandez C, Fiandor A, Martinez-Garate A, Martinez Quesada J.     Allergy to pistachio: crossreactivity between pistachio nut and     other Anacardiaceae. Clin Exp Allergy 1995; 25: 1254-9. -   6. Parra F M, Cuevas M, Lezaun A, Alonso M D, Beristain A M,     Losada E. Pistachio nut hypersensitivity: identification of     pistachio nut allergens. Clin Exp Allergy 1993; 23: 996-1001. -   7. Burks A W, Shin D, Cockrell G, Stanley J S, Helm R M, Bannon G A.     Mapping and mutational analysis of the IgE-binding epitopes on Ara h     1, a legume vicilin protein and a major allergen in peanut     hypersensitivity. Eur J Biochem 1997; 15; 245: 334-9. -   8. Chomczynski P., Sacchi N. Single step method of RNA isolation by     acid guanidinium thiocyanate-phenol-chloroform extraction. Anal     Biochem 1987; 162: 156-9. -   9. Sze-Tao K W C, Schrimpf J., Teuber S S, Roux K H, Sathe S K.     Effects of processing and storage on walnut (Juglans regia L.)     tannins. J Sci Food Agric 2001; 81: 1215-22. -   10. Robotham J M, Teuber S S, Sathe S K, Roux K H Linear IgE epitope     mapping of the English walnut (Juglans regia) major food allergen,     Jug r 1. J Allergy Clin lmmunol 2002; 109: 143-9. -   11. Marcus J P, Green J L, Goulter K C, Manners J M. A family of     antimicrobial peptides is produced by processing of a 7S globulin     protein in Macadamia integrifolia kernels. Plant J. 1991; 19:     699-710 -   12. Belanger F C, Kriz A L. Molecular basis for allelic polymorphism     of the maize Globulin-1 gene. Genetics 1991; 129: 863-72 -   13. Belanger F C, Kriz A L. Molecular characterization of the major     maize embryo globulin encoded by the Glb1 gene. Plant PhysioL 1989;     91: 636-43. -   14. Grimes H D, Overvoorde P J, Ripp K, Franceschi V R, Hitz W D. A     62-kD sucrose binding protein is expressed and localized in tissues     actively engaged in sucrose transport. Plant Cell. 1992; 4: 1561-74. -   15. Teuber S S, Jarvis K C, Dandekar A M, Peterson W R, Ansari A. A.     Cloning and sequencing of a gene encoding a vicilin-like protein,     Jug r 2, from English walnut kernel (Juglans regia): a major food     allergen. J Allergy Clin Immunol 1999; 104: 1311-20. -   16. Rabjohn P, Helm E M, Stanley J S, West C M, Sampson H A, Burks A     W, Bannon G A. Molecular cloning and epitope analysis of the peanut     allergen Ara h 3. J Clin Invest. 1999; 103: 535-42. -   17. Helm R M, Cockrell G, Connaughton C, West C M, Herman. E,     Sampson H A, Bannon G A, Burks A W. Mutational analysis of the     IgE-binding epitopes of P34/Gly m Bd 30K. J Allergy Clin Immunol.     2000; 105: 378-84. -   18. Stanley J S, King N, Burks A W, Huang S K, Sampson H, Cockrell     G, Helm R M, West C M, Bannon G A. Identification and mutational     analysis of the immunodominant IgE binding epitopes of the major     peanut allergen Ara h 2. Arch Biochem Biophys 1997; 342: 244-53. -   19. Beezhold D H, Hickey V L, Sussman G L. Mutational analysis of     the IgE epitopes in the latex allergen Hev b 5. J Allergy Clin     Immunol. 2001; 107: 1069-76. -   20. Heiss S, Mahler V, Steiner R, Spitzauer S, Schweiger C, Kraft D,     Valenta R. Component-resolved diagnosis (CRD) of type I allergy with     recombinant grass and tree pollen allergens by skin testing. J     Invest Dermatol. 1999; 113: 830-7. -   21. Valenta R, Vrtala S, Focke-Tejkl M, Bugajska-Schretter, Ball T,     Twardosz A, Spitzauer S, Gronlund H, Kraft D. Genetically engineered     and synthetic allergen derivatives: candidates for vaccination     against type I allergy. Biol Chem 1999; 380: 815-24 -   22. Bannon G A, Cockrell G, Connaughton C, West C M, Helm R, Stanley     J S, King N, Rabjohn P, Sampson H A, Burks A W. Engineering,     characterization and in vitro efficacy of the major peanut allergens     for use in immunotherapy. Int Arch Allergy Immunol 2001; 124; 70-2. -   23. Niederberger V, Stubner P, Spitzauer S, Kraft D, Valenta R,     Ehrenberger K, Horak F. Skin test results but not serology reflect     immediate type respiratory sensitivity: a study performed with     recombinant allergen molecules. J Invest Dermatol. 2001; 117:     848-51. -   24. Bhalla P L, Swoboda I, Singh M B. Reduction in allergenicity of     grass pollen by genetic engineering. Int Arch Allergy Immunol 2001;     124: 51-4. -   25. Nordlee J A, Taylor S L, Townsend J A, Thomas L A, Bush R K.     Identification of a Brazil-nut allergen in transgenic soybeans. New     Engl J Med 1996; 334: 688-92. -   26. Maleki S J, Kopper R A, Shin D S, Park C W, Compadre C M,     Sampson H, Burks A W, Bannon G A. Structure of the major peanut     allergen Ara h 1 may protect IgE-binding epitopes from degradation.     J Immunol 2000; 164: 5844-9 -   27. van Kampen V, Becker W M, Chen Z, Rihs H P, Mazur G, Raulf M,     Liebers V, lsringhausen-Bley S, Baur X. Analysis of B-cell epitopes     in the N-terminal region of Chi t I component III using monoclonal     antibodies. Mol Immunol. 1994; 31: 113340. -   28. Breiteneder H, Ferreira F, Reikerstorfer A, Duchene M, Valenta     R, Hoffmann-Sommergruber K, Ebner C, Breitenbach M, Kraft D,     Scheiner O. Complementary DNA cloning and expression in Escherichia     coli of Aln g I, the major allergen in pollen of alder (Alnus     glutinosa). J Allergy Clin Immunol. 1992; 90: 909-17. -   29. Ball G, Shelton M J, Walsh B J, Hill D J, Hosking C S, Howden     M E. A major continuous allergenic epitope of bovine     beta-lactoglobulin recognized by human IgE binding. Clin Exp     Allergy. 1994; 24: 758-64. -   30. Aas K, Elsayed S. Physico-chemical properties and specific     activity of a purified allergen (codfish). Dev Biol Stand 1975; 29:     90-8. -   31. Elsayed S, Holen E, Dybendal T. Synthetic allergenic epitopes     from the amino-terminal regions of the major allergens of hazel and     birch pollen. Int Arch Allergy Appl Immunol. 1989; 89: 410-5. -   32. Herian A M, Taylor S L, Bush R K. Identification of soybean     allergens by immunoblotting with sera from soy-allergic adults. Int     Arch Allergy Appl Immunol. 1990; 92: 193-8. -   33. Shanti K N, Martin B M, Nagpal S, Metcalfe D D, Rao P V.     Identification of tropomyosin as the major shrimp allergen and     characterization of its IgE-binding epitopes. J Immunol 1993; 151:     5354-63. -   34. Schramm G, Bufe A, Petersen A, Haas H, Merget R, Schlaak M,     Becker W M Discontinuous IgE-binding epitopes contain multiple     continuous epitope regions: results of an epitope mapping on     recombinant Hol I 5, a major allergen from velvet grass pollen. Clin     Exp Allergy. 2001; 31: 331-41. -   35. Vila, L., Beyer K, Jarvinen K M, Chatchatee P, Bardina, L,     Sampson H A. Role of conformational and linear epitopes in the     achievement of tolerance in cow's milk allergy. Clin Exp Allergy     2001; 31: 1599-1606. -   36. Bredehorst R, David K. What establishes a protein as an     allergen? J Chrom B 2001; 756: 33-40. -   37. Sicherer, S H, Furlong T J, Munoz-Furlong A. Burks A W, Sampson     H A. A voluntary registry for peanut and tree nut allergy:     Characteristics of the first 5149 registrants. J Allergy Clin     Immunol 2001; 108: 128-32. -   38. Pelikan Z. The diagnostic approach to immediate hypersensitivity     in patients with allergic rhinitis; a comparison of nasal challenges     and serum RAST. Ann Allergy 1983; 51: 395-400. -   39. Bousquet J, Lebel B, Dhivert H, Bataille Y, Martinot B, Michel     F B. Nasal challenge with pollen grains, skin-prick tests and     specific IgE in patients with grass pollen allergy. Clin Allergy     1987; 17: 529-36 -   40. Rasanen L, Kuusisto P, Penttila M, Nieminen M, Savolainen J,     Lehto M. Comparison of immunologic tests in the diagnosis of     occupational asthma and rhinitis. Allergy. 1994; 49: 342-7.

SUMMARY OF THE INVENTION

With the foregoing in mind, the present invention advantageously provides purified linear epitope polypeptide sequences from cashews, nucleic acid sequences encoding therefor, and associated methods employing the discovered sequences.

There has been considerable interest in recent years in precise biochemical and immunological characterization of allergens for possible application to immunotherapy, clinical screening and immunoassay development.¹⁸⁻²¹ Moreover, new advances in plant genetic engineering may allow the for the alteration of plant proteins to generate hypoallergenic cultivars.²² Not only is it important to identify allergens for possible modification in host plants but there is a need for information on the potential for allergenicity of the products of genes that are to be transferred to unrelated hosts for nutritional, processing or management purposes as witnessed by the ill-fated attempt to transfer Brazil nut 2S albumin genes to certain crops.²³ It is thus important that as many food allergens as possible, both major and minor, be identified to add to this database of information.

An invaluable method for allergen identification relies on the screening of cDNA libraries produced from the offending tissue and screened with allergen-specific antibody. We have applied this approach to the identification of the precursor of a cashew allergen, designated Ana o 1, another allergen of the vicilin-like protein family. The 7S globulins from legumes are referred to as vicilins and are seed storage proteins which often exist as large trimeric oligomers in the seed protein bodies with individual subunits usually 40-70 kDa in size. Peanut vicilin, Ara h 1, has been shown to resist proteolysis when in a trimeric configuration, a property which may contribute to its allergenicity.²⁴ Globulin proteins from several non-leguminous plant seeds have been found to have significant sequence homology to the vicilins and can thus be designated as part of the vicilin group of proteins (vicilin-like), such as the previously described walnut (Juglans regia) tree nut allergen, Jug r 2.¹³

The unique IgE-binding patterns of each pool of sera to the Ana o 1 epitopes suggests a heterogeneity of recognition patterns between patients though some peptides were recognized by members of two or all three pools. Perhaps significantly, the most strongly reacting peptides were the three recognized by the sera in all three pools with the exception of epitope #6 which was strongly recognized only by pool one.

Multiple linear IgE-binding epitopes residing on one allergenic peptide have been observed in many other cases of foods known to cause immediate hypersensitivity reactions²⁵⁻³¹ though we recently reported finding only a single linear epitope on the walnut 2S albumin, Jug r 1.¹⁰ The fact that most allergens have multiple IgE-binding sites is at least partly due to the polyclonal nature of the immune response to these allergens.¹⁶

When considered together, conformational and linear epitopes may cover the entire surface of some allergens (i.e., Hol h 1 grass allergen).³² Interestingly, the linear epitopes rather than the conformational epitopes have been reported to be better predictors of allergy persistence as in cow's milk allergy.³³

To date, no common structural characteristics of linear-IgE epitopes have been identified (reviewed in³⁴), but this could change as more epitope mapping studies are completed. Cashew Ana o 1 and the major allergen in peanuts, Ara h 1, are both vicilins and both express multiple epitopes, in fact, 23 linear epitopes have been described for Ara h 1.⁷ In parallel with the observations on Ara h 1, we did not observe any obvious sequence motifs that are shared by any two linear epitopes within the Ana o 1. Surprisingly, even though these two proteins share 27% identity and 45% similarity in amino acid sequence and presumably are similar in overall structure, there was no significant sequence conservation between epitopes of the two allergens. Moreover, even though three epitopes toward the C-terminal end of the compared sequences showed positional overlap, most of the rest did not. Though it is still possible that conformational (discontinuous) epitopes could be shared in common, these remarkable observation may help explain the lack of crossreactivity between tree nut and peanut reactive patients' sera³⁵.

Based on our previous immunoblotting of cashew proteins, it is known that major allergens are located in the 2S albumin protein family and the legumin family. Interestingly, our cDNA library constructed late in maturation appears to have overwhelmingly contained mRNA for the vicilin-like storage protein. This protein is a major allergen by definition (bound by ≧50% of allergic patients). Since several studies have shown that there is no direct correlation between binding strength in in vitro assays and in vivo reactivity^(21,36-38), the relative importance of this protein among the various cashew proteins responsible for the allergic reaction in sensitive patients is yet to be determined. Efforts are underway to clone cDNAs encoding the additional allergenic cashew seed storage proteins.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the features, advantages, and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, presented for solely for exemplary purposes and not with intent to limit the invention thereto, and in which:

FIG. 1 shows in A the nucleotide sequences of cDNA clones of Ana o 1.0101 (Ao1.1) SEQ ID NO: 1 and Ana a 1.0102 (Ao1.2) SEQ ID NO: 2, and in B the amino acid sequences of their respective polypeptides (Ao1.1), SEQ ID NO: 3. and (Ao1.2), SEQ ID NO: 4, according to an embodiment of the present invention; the N-terminal amino acid of the recombinant peptides, Ana a 1a and Ana o 1b, are indicated (&Hat;); the presumed allelic difference between the 2 genes is indicated in bold type; the presumed start and stop codons are underlined; asterisks denote identity; GenBank accession numbers are AF395893 and AF395894;

FIG. 2 shows a Western blot identification of native Ana o 1 polypeptide of the present invention; nitrocellulose blots of total cashew extract probed with rabbit anti-cashew extract antiserum (Ra) and human serum from a patient with cashew allergy (no. 9, Hu) are shown: lanes 1, 3, and 5, no inhibitor added (−); lanes 2 and 4, 5 μg of purified rAna o 1 preincubated and coincubated with anti-sera; lane 6.5 μg of recombinant MBP preincubated and coincubated with antisera; arrow indicates inhibited band in lanes 2 and 4; and

FIG. 3 compares linear epitope maps of cashew Ana o 1 with peanut Ara h 1⁷; epitopes are numbered, and larger boxes depict epitopes that overlap within a sequence. Sequences of epitopes showing positional overlap between Ana o 1 and Ara h 1 are shown for comparison; asterisks indicate breaks in sequence bars corresponding to 132-amino-acid epitope-free regions in each sequence: I. indicates identical amino acids; and •, indicates similar amino acids.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including any definitions, will control. In addition, the materials, methods and examples given are illustrative in nature only and not intended to be limiting. Accordingly, this invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these illustrated embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.

Terms Employed

List of Acronyms and Abbreviations Used.

DTT: dithiothreitol

EDTA: ethylenediamine tetraacetic acid

HRP: horseradish peroxidase

PCR: polymerase chain reaction

PBS: phosphate buffered saline

RAST: radioallergosorbent test

SDS-PAGE: sodium dodecyl sulfate polyacrylamide gel electrophoresis

TBS: tris-buffered saline

RT: room temperature

Isolated Nucleic Acid. An “isolated nucleic acid” is a nucleic acid the structure of which is not identical to that of any naturally occurring nucleic acid or to that of any fragment of a naturally occurring genomic nucleic acid spanning more than three separate genes. The term therefore covers, for example, the following:

a) a DNA whose sequence is part of a naturally occurring genomic DNA molecule but which is not associated with the coding sequences that would normally lie adjacent the sequence in the naturally occurring genome of the organism of origin;

b) a nucleic acid sequence inserted in a vector or in the genome of a prokarytic or eukaryotic cell so as to result in a nucleic acid molecule different from a naturally occurring vector or the natural genomic DNA;

c) a discrete molecule such as a CDNA, or a fragment such as a genomic fragment, one produced by the polymerase chain reaction (PCR), or a fragment produced by a restriction enzyme; and

d) a recombinant nucleotide sequence forming part of a hybrid gene, for example, a gene encoding a fusion protein.

Mutation by substitution. A mutation by substitution is generally intended to mean a conservative substitution, which is the replacement of one amino acid residue with a different residue having similar biochemical characteristics, such as size, charge, and polarity vs. nonpolarity.

Methods

Human sera. Blood samples were drawn after informed consent from patients with life-threatening systemic reactions to cashew nut and the sera frozen at −70° C. until use. The study was approved by the human subjects review committee of the University of California at Davis. The presence of cashew-reactive IgE was confirmed by Pharmacia ImmunoCAP assay or by Western immunoblotting as described below. Control sera were obtained from patients with a history of anaphylaxis to walnut, pistachio or hazelnut who reported tolerance of cashews.

Cashew protein extract. An albumin/globulin extract was prepared as previously described.⁷ Protein concentrations were measured by use of the Bradford protein assay (BioRad Laboratories, Inc., Hercules, Calif.).

Production of rabbit polyclonal antiserum. A rabbit was immunized with 5 mg of cashew extract in Freund's complete adjuvant and boosted four weeks later with 5 mg of cashew extract in incomplete Freund's adjuvant. The rabbit was subsequently bled and the serum stored at −20° C. Construction and IgE immunoscreening of cashew cDNA library. Four cashew nuts in late maturation were chopped, frozen in liquid nitrogen, and ground with a mortar and pestle. Total RNA was extracted in TRIzol (GIBCO BRL Life Technologies Inc., Rockville, Md.) as previously described⁸ and mRNA was isolated using a PolyATtract kit (Promega, Madison, Wis.) according to the manufacturers instructions. The construction of the cDNA library was performed using the Uni-ZAP XR Gigapack Cloning Kit (Stratagene Inc., Cedar Creek, Tex.) following the manufacturer's instructions. The double-stranded cDNAs with EcoR I (using a 5′ end adapter) and Xho I (using a 3′ end PCR primer) cohesive ends were cloned into the lambda Uni-ZAP XR expression vector. The library was amplified on E. coli strain XL1-Blue. The amplified library was initially screened with rabbit anti-cashew serum at 1:5,000 dilution. Bound IgG was detected using HRP-conjugated goat anti-rabbit IgG antibody (Sigma, St. Louis, Mo.) at 1:50,000 dilution and developed with the ECL Plus chemiluminescent kit (Amersham Pharmacia Biotech Inc., Piscataway, N.J.). Clones were subsequently screened with antiserum from a cashew-allergic patient (at 1:20 dilution) and detected using HRP-conjugated goat anti-human IgE antibody (Biosource International, Camarillo, Calif.) at 1:2000 dilution and developed with ECL. The immunopositive clones were picked, plaque-purified, and stored in SM buffer supplemented with 2% chloroform at 4° C. Sequencing and corresponding analysis of selected genes. Inserts from the selected phage clones were amplified with M13 forward and reverse primers by PCR. Both strands of the PCR products were then sequenced on an ABI 3100 Genetic Analyzer (Foster City, Calif.) using capillary electrophoresis and Version 2 Big Dye Terminators as described by the manufacturer. Similarity searches and alignments of deduced amino acid sequences were performed on Genetics Computer Group (GCG) software (Accelrys, Inc. San Diego, Calif.) using the basic local alignment search tool (BLAST) program. Cloning, expression and purification of cDNA-encoded proteins. cDNA coding sequences were modified by the addition of an Xba I site at 5′ end and an Pst I site at 3′end by PCR using PfuTurbo DNA polymerase (Stratagene Inc., Cedar Creek, Tex.). followed by digestion and ligated to their respective sites of the maltose binding protein (MBP) fusion expression vector pMAL-c2 (New England BioLabs Inc., Beverly, Mass.), containin a thrombin cleavage site.

Competent E. coli BL21 (DE3) cells (Novagen Inc., Madison, Wis.) were transformed with cDNA/pMAL-c2 plasmids, and single colonies grown at 37° C. to an OD₆₀₀ of 0.5, and induced with isopropyl-D-thiogalactopyranoside (IPTG). The cells were harvested, resuspended in amylose resin column buffer (20 mM Tris-HCI; pH 7.4, 200 mM NaCI, 10 mM P-mercaptoethanol, 1 mM EDTA), lysed with mild sonication, centrifuged at 12,000 g, passed over an amylose affinity column and the fusion protein eluted with column buffer containing 10 mM maltose. Fusion proteins were cleaved with thrombin (Sigma, St. Louis, Mo.) at 1 mg of fusion protein/1 of thrombin in column buffer (3 hr, RT). The liberated recombinant protein was purified by HPLC on a Superdex 200 column (Amersham Pharmacia, Piscataway, N.J.) concentrated, and either stored (briefly) at 4° C. until use or frozen at −70° C.

Polyacrylamide gel electrophoresis (PAGE) and protein transfer. Recombinant protein or cashew extract samples were subjected to SDS-PAGE (12%) with 0.5 μg recombinant protein or 200 to 300 μg total cashew extract per 4 mm well width and used for immunoblotting as previously described.⁹ IgE Western Immunoblotting and Inhibitions.

Strips (34 mm wide) of blotted nitrocellulose which were blocked for 1 hour at RT in phosphate buffered saline (PBS)/3% nonfat dry milk/0.2% Triton X-100 (TX-100). Diluted sera (1:5 v:v in the blocking buffer, but 1:20 v:v was used for highly reactive sera) were added to the strips and incubated overnight at RT. The strips were then washed for 20 minutes three times in PBS/0.01% TX-100 and incubated overnight at RT with equine polyclonal ¹²⁵I-anti-human IgE (Hycor Biomedical Inc., Garden Grove, Calif.) diluted 1:5 in the nonfat milk buffer. The strips were washed as above and exposed to x-ray film (Kodak X-OMAT).

For inhibition experiments, 10 ug of recombinant Ana o 1 (with and without associated MBP) were pre incubated with human or rabbit antisera. Human antiserum (from patient #9 at 1:20 dilution) or rabbit antiserum (at 1:5000 dilution) were incubated with Ana o 1 for 1 hr at 37° C. and then incubated with NC strips containing blotted cashew extract overnight at 4° C. Controls included strips incubated with human or rabbit antisera without added Ana o 1, and with normal human and rabbit serum. The strips were then washed for 15 min followed by three 5 min washes in TBS-T and incubated with goat anti-rabbit IgG-HRP (Sigma, St. Louis, Mo.) at 1:50,000 in TBS-T for 1 hr at RT or ¹²⁵I anti-human IgE at 1:10 in PBS-T with 5% dried milk overnight at 4° C. The strips were washed as above and, for human antibody, the reactive bands identified by exposure to x-ray film (Kodak X-OMAT) directly or, for rabbit antibody, developed using ECL-Plus chemiluminescence kit (Amersham Pharmacia Biotech, Inc, Piscataway, N.J.), as described by the manufacturer, followed by exposure to x-ray film (Kodak X-OMAT).

N-terminal amino acid sequencing. SDS-PAGE was carried out as above on reduced cashew polypeptides, using a 10% acrylamide gel, and proteins were transferred to Trans-Blot PVDF membrane (0.2 μm) (BioRad). The N-terminal sequence of the approximately 50 kD protein was determined using blotted protein on an ABI 477A sequencer with an on-line 120A HPLC system (Applied Biosystems, Inc., Foster City, Calif.). Internal tryptic digests after carboxymethylation were performed on the bands from a wet acrylamide gel, separated by ABI 173 Microbore HPLC, and then sequenced as above. Sequence data were collected utilizing ABI Procise software (Applied Biosystems, Inc.) and analyzed with FASTA programming (European Bioinformatics Institute). Solid-phase peptide (SPOTs) synthesis and binding to IgE. Based on the derived amino acid sequence of the 540 amino acid Ana o 1 protein, 66 overlapping 15-amino acid peptides, each offset by eight amino acids, were synthesized and probed with pooled patients' sera diluted 1:5 (v:v) in Genosys blocking buffer followed by washing) incubation with ¹²⁵I-anti-human IgE (Hycor Biomedical Inc.) and 48 hr exposure at −70° C. to Kodak Biomax x-ray film as previously described.¹⁰

Results

Library screening and gene characterization. The initial screening included separate probings with human serum (IgE immunodetection) and rabbit antisera (IgG immunodetection). Clones that gave positive signals for both probes were selected, as one of our future goals is to determine the degree of epitope overlap between these two species. A total of 50 clones were selected of which four were purified and sequenced. The four clones varied in length from 1699 to 1781 nt, excluding the poly-A tails. Comparison of the sequences revealed that three differed only in the length of their 3′ ends. A fourth shared a common 3′ end but its 5′ end was truncated and fused via an adapter sequence with another apparently unrelated cDNA sequence showing homology with plant ABA-responsive protein (data not shown). Gene Ao1.1 (shown in FIG. 1A) represents the longest version of the cDNAs and Ao1.2 is the truncated version. Note that only a single nucleotide substitution (A for G) at residue 994 distinguishes Ao1.1 and Ao1.2 in their region of common overlap suggesting that this represents an allelic difference. Protein sequence characterization. Analysis of the deduced amino acid sequence revealed a 540 aa open reading frame, a possible start codon at position 3, and possible leader peptide from 3 to 28 (FIG. 1B). Probing of the selected clones by PCR using an internal (Ao1-specific) primer paired with a vector primer to amplify the 3′ ends of the cDNA inserts revealed that all but two of the remaining 46 plaques were Ao1-like and each produced an amplicon similar in size to Ao1 (data not shown).

A search of Genbank revealed that Ao1.1 and Ao1.2 encode members of the 7S (vicilin) superfamily of proteins. Sequences with the highest aa identity and similarity were in the 33% to 43% and 52% to 62% range, respectively, and were variously described as vicilins and sucrose-binding proteins and their precursors, and 7S globulins from nut and seed crops (Table 1).¹¹⁻¹³

Reactivity of the recombinant protein with human IgE and rabbit IgG. For immunological characterization, we cloned a long version of the Ao1.1 cDNA (designated Ao1.1a) beginning (at K29) after the presumptive leader peptide, and a short version (Ao1.1b), beginning with the methionine residue 102 (M102) (FIG. 1B). The DNA segments were ligated into an expression vector designed to allow for purification of the recombinant molecules by way of a mannose-binding protein fusion domain in conjunction with an amylose affinity column and a thrombin-specific cleavage site. The resulting ˜105 kD, and ˜93 kD fusion proteins Ana o 1a and b, respectively, were affinity purified and digested with thrombin to yield ˜65 and ˜55 kD peptides, respectively, as well as the 43 kD MBP. Both cleaved and uncleaved peptides were reactive with specific human IgE and rabbit IgG. Recognition of Ana o 1 as an allergen. The prevalence of reactivity to rAna o 1 among cashew allergic patients by Western immunoblotting is shown in Table II. IgE from 10 of 20 sera from patients with a history of life-threatening reactions to cashews bound the recombinant. In four cases, the intensity of the signal was strong, but was weak in seven cases, implying though not proving, variable titers of antibody directed to this protein. In contrast, 2 of 8 sera from patients tolerant of cashew but clinically with life-threatening reactions to other tree nuts reacted with the rAna o 1. One of these (#22) showed weak binding (the patient self-reported mild throat scratchiness with cashew) while the other (#21) showed strong binding yet the patient reconfirmed no symptoms upon cashew ingestion but has had four emergency department visits after accidental walnut or pecan ingestion, and recent strong wheals and flare reaction to walnut and cashew upon skin prick testing. Identification of native Ana o 1 by SDS-PAGE immunoblotting. To identify the band or bands in a typical total cashew immunoblot that correspond to the cloned polypeptide storage protein precursor we attempted to inhibit the binding of sera from a cashew extract-immunized rabbit and allergic patient #9 to nitrocellulose strips blotted with total soluble cashew extract using putified rAna o 1 as the inhibitor (FIG. 2). No inhibitor was added to the antisera used to probe the left strip in each pair (lanes 1, 3 and 5) whereas the antisera used to probe the right strip in each pair (lanes 2 and 4) was pre- and co-incubated with 5 ug of purified rAna o 1 protein. Serum used in lane six was pre- and co-incubated with 5 ug of rMBP. It can be seen that recombinant protein inhibits IgE binding to a band of molecular mass ˜50 kD. Similar results were seen when undigested rAna o 1/MBP was used as the inhibitor (data not shown). Thus, the native precursor, corresponding to our ˜65 kD recombinant protein, appears to undergo further cleavage as in other vicilin group proteins. Identification of native Ana o 1 by sequencing. N-terminal sequencing of the band identified the immunoblot inhibition was uninformative, however, one of the internal tryptic digest peptide showed 100% homology with the translated aa sequence of Ana o 1 from position 295 to 306 in SEQ ID NO:1. Identification and recognition of IgE-reactive linear epitopes on Ana o 1 and comparison to peanut vicilin linear epitopes. The entire amino acid length of Ana o 1 was studied by probing overlapping solid phase synthetic peptides with sera from 12 patients randomly assigned to three pools. Collectively, the three pools reacted with 11 linear IgE-binding epitopes which were distributed throughout the length of the protein (Table III). Three of the identified epitopes were bound by patients' sera from all three pools. Epitope #4 was bound strongly by pools 1 and 2, and moderately by pool 3. Epitope #11 was bound strongly by pool 2, but only moderately by pools 1 and 3. The third epitope, # 1, was bound moderately by all three pools. Some epitopes gave moderate (#'s 2, 3, 7, 8, 9, 10) or strong (#6) signals only when probed with pool 1. Similarly, epitope # 5 was moderately recognized only by pool 2.

To compare the recognized linear epitopes of cashew vicilin (Ana o 1) to those of peanut vicilin (Ara h1)⁷ we aligned the two sequences using the BLAST program and highlighted the corresponding linear epitopes (diagramed in FIG. 3). Of the regions that were included in the BLAST alignment (1-528 of 540 amino acids for Ana o 1 and 1-587 of 626 for Ara h 1), only four of the 11 Ana o 1 and 23 Ara h I linear epitopes showed significant (≧7 amino acids) positional overlap. Even among the overlapping epitopes there was no significant homology or similarity between the Ana o1 and Ara h 1 sequences considering that a single amino acid substitution usually eliminates reactivity in allergens.^(7.10,14-17)

The Various Aspects of the Claimed Invention.

The present invention discloses isolated nucleic acid sequences, polypeptide products thereof, and associated methods. The skilled will recognize that the isolated nucleic acids will be useful at least when expressed in a suitable cell or organism to produce the encoded polypeptides, which in turn may be employed in testing to identify patients allergic to cashew nuts. Furthermore, expression of the nucleic acid sequences of the present invention in a suitable cell may be useful in studying and characterizing gene function.

Accordingly, the present invention includes an isolated nucleic acid sequence comprising the nucleotide sequence of SEQ ID NO:1, or a degenerate variant of SEQ ID NO:1. The nucleic acid sequence described may also comprise at least one mutation selected from a deletion, a substitution, and an addition. A preferred embodiment of the invention includes an expression vector comprising the nucleic acid sequence noted above operably linked to an expression control sequence, and a cultured cell comprising this vector, the cell, or a progeny of the cell, preferably being transfected with the vector, wherein the cell expresses a polypeptide encoded by said nucleic acid sequence. Conversely, the invention further includes an isolated nucleic acid comprising a sequence that encodes a polypeptide comprising the amino acid sequence of SEQ ID NO:3.

An additional aspect of the invention includes a method of producing a protein, comprising culturing the cell comprising nucleic acid sequence SEQ ID NO:1 under conditions permitting expression of a polypeptide encoded by the nucleic acid. The method may also include purifying the polypeptide from the cell or the medium of the cell.

As noted above for SEQ ID NO:1, the invention also includes an isolated nucleic acid sequence comprising the nucleotide sequence of SEQ ID NO:2, or a degenerate variant of SEQ ID NO:2. The nucleic acid sequence described may also comprise at least one mutation selected from a deletion, a substitution, and an addition. A preferred embodiment of the invention includes an expression vector comprising the nucleic acid sequence SEQ ID NO:2 operably linked to an expression control sequence, and a cultured cell comprising this vector, the cell, or a progeny of the cell, preferably being transfected with the vector, wherein the cell expresses a polypeptide encoded by said nucleic acid sequence. Conversely, this embodiment of the invention further includes an isolated nucleic acid comprising a sequence that encodes a polypeptide comprising the amino acid sequence of SEQ ID NO:4.

Yet another method aspect of the invention includes a method of producing a protein, comprising culturing the cell comprising SEQ ID NO:2, or a degenerate variant thereof, under conditions permitting expression of a polypeptide encoded by said nucleic acid. As previously noted, the method may also include purifying the polypeptide from the cell or the medium of the cell.

The invention also discloses eleven (11) linear polypeptide epitopes, as listed in Table III, which are also respectively listed herein as SEQ ID NO:5 through SEQ ID NO:15. Accordingly, the invention includes an isolated nucleic acid comprising a sequence that encodes a polypeptide comprising an amino acid sequence selected from SEQ ID NOS:5-15. Additionally claimed is a purified Ig-E binding immunogenic polypeptide the amino acid sequence of which comprises at least one sequence selected from SEQ ID NOS:3-15, and wherein the polypeptide comprises at least one mutation in said selected amino acid sequence, the mutation being selected from a deletion, a substitution, an addition, and particularly a mutation which reduces the polypeptide's IgE-binding capacity but retains at least some immunogenicity. Those skilled in the art should recognize that the scope of the invention includes an isolated nucleic acid sequence or a degenerate variant thereof, which encodes a polypeptide consisting essentially of an amino acid sequence selected from SEQ ID NOS:3-15, and that the selected amino acid sequence may include at least one mutation such as a deletion, a substitution, or an addition. It should be understood that by “essentially” it is meant that the polypeptide is largely, but not wholly, the specified sequence.

Further method aspects of the disclosed invention include a test for detecting a cashew allergy in a patient, said test comprising contacting the patient with an amount of a purified polypeptide comprising at least one amino acid sequence selected from SEQ ID NOS:3-15. In this test, contacting preferably comprises injecting the patient with the purified polypeptide. The skilled will know that injecting includes any of the known routes useful in immunological testing of patients, for example, intradermally, and subcutaneously. Additionally, the purified polypeptide for use in such a test may comprise at least one mutation in said amino acid sequence, and the mutation may be selected from a deletion, a substitution, and an addition.

Yet a further diagnostic test of the invention for detecting anti-cashew IgE in a patient to thereby indicate an allergy to cashews, the test comprising several steps. The patient's serum is reacted with a purified polypeptide the amino acid sequence of which comprises at least one sequence selected from SEQ ID NOS:3-15. The polypeptide is separated from unreacted patient serum, and the polypeptide is reacted with a labeled human IgE-reactive agent after separating from unreacted patient serum. The polypeptide is then separated from unreacted labeled human IgE-reactive agent, and the labeled human IgE-reactive agent bound to the polypeptide after separating from unreacted agent is detected directly or indirectly to thereby indicate presence in the patient's serum of anti-cashew IgE. The amino acid sequence of the polypeptide for use in this test may also comprise at least one mutation selected from a deletion, a substitution, and an addition.

A test for screening patients for allergy to cashews may be embodied in a test kit comprising a first reagent containing at least one purified polypeptide whose amino acid sequence comprises at least one sequence selected from SEQ ID NOS:3-15. The test kit preferably also includes a second reagent containing at least one labeled human IgE-reactive agent. Additionally, in the test kit the first reagent may include a solid phase carrying the purified polypeptide.

The skilled will find additional guidance in carrying out the invention by consulting Sambrook et al., 1989, Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Press, N.Y., and also Ausubel et al. (eds.), 1995, Current Protocols in Molecular Biology (John Wiley & Sons, N.Y.). In addition, guidance in diagnostic and screening test methods suitable for use with the polypeptides of the present invention may be found in Manual of Clinical Laboratory Immunology, Sixth Edition, Rose et al. (eds.), 2002, American Society for Microbiology, Washington, D.C. These publications are incorporated herein in their entirety.

In the drawings and specification, there have been disclosed a typical preferred embodiment of the invention, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The invention has been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the invention as described in the foregoing specification and as defined in the appended claims.

TABLE I Proteins showing identity and similarity to Ana o1 Amino Accession acid Simi- Protein Organism no. overlap Identity larity 7S globulin Elaeis guineensis AAK28402  6-524 40% 59% (African oil palm) Vicilin Macadamia AAD54246 35-538 37% 57% precursor¹¹ intergrifolia (macadamia nut) Sucrose- Pisum sativum TO6459 95-538 43% 62% binding (garden pea) protein homolog Sucrose- Glycine max Q04672  3-539 36% 52% binding (soybean) protein precursor¹² Vicilin-like Juglans regia AF066055 33-537 33% 54% protein (English walnut) precursor¹³

TABLE II IgE Western blot reactivity with rAna o 1 Cashew allergy Cashew tolerance Subject no. Reactivity Subject no. Reactivity 1 − 21 +++ 2 − 22 + 3 +++ 23 − 4 − 24 − 5 − 25 − 6 + 26 − 7 + 27 − 8 − 28 − 9 +++ 10 − 11 + 12 − 13 − 14 +++ 15 + 16 + 17 + 18 + 19 − 20 −

Table II

TABLE III Ana o 1 IgE-binding epitopes Pool reactivity† Ana o 1 Pool Pool Pool Epitope no. Amino acid sequence* position 1 2 3 1 AIMGPPTKFSFSLFL  1-15 ++ ++ + 2 CKVQRQYDEQQKEQC 41-55 + − − 3 EQQKEQCVKECEKYY 49-53 + − − 4 KECEKYYKEKKGRER 57-71 +++ +++ +++ 5 EKKGREREHEEEEEE 65-79 − ++ − 6 DEAEEEDENPYVFED 145-159 +++ − − 7 RRCEGPKIWPFTEES 337-351 ++ − − 8 NITKGGMSVPFYNSR 393-407 + − − 9 TKIAIVVSGEGCVEI 409-423 + − − 10 SSHPSYKKLRARIRK 433-447 + − − 11 EEFFFQGPEWRKEKE 521-535 + +++ + +++, strong binding: ++, moderate binding: +, weak binding. *Peptides believed to be immunodominant epitopes are shown in bold. †Pool 1 was composed of patients 3, 7, 9, and 23; pool 2 was composed of patients 4, 11, 14, 15, and 18; and pool 3 was composed of patients 6, 17, and 21. 

1. A purified IgE binding immunogenic polypeptide the amino acid sequence of which consists of SEQ ID NO:8.
 2. A test kit for screening patients for allergy to cashews, said kit comprising a first reagent containing at least one purified IgE binding polypeptide consisting of SEQ ID NO:8.
 3. The test kit of claim 2, further comprising a second reagent containing at least one labeled anti-human IgE antibody.
 4. The test kit of claim 2, wherein said first reagent further comprises a solid phase carrying the polypeptide. 